Volume 21, Issue 1, Pages 41-43 (February 2010)

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Continuing professional development: Bariatric MCQs and self assesment

Article Outline

• Bariatric MCQ answers

• SAQ answers

• Clinical scenario answers

Bariatric MCQ answers

1.Answers a b c d

2.Answers a c d e

Thrombo embolism is a significant issue. Venous thrombo-embolism (VTE) accounts for the majority of deaths in patients undergoing bariatric surgery.

3.Answers b

Juvin et al., a Mallampati score of 3 or 4 was an independent risk factor. Reduced mouth opening (inter-incisor gap) has not been found to be a significant independent predictor of difficult intubation in the obese. OSA has not been shown to be an independent risk factor for difficult intubation.

Gaszynski T. Standard clinical tests for predicting difficult intubation are not useful among morbidly obese patients. Anesth Analg 2004;99: 956.

4.Answers a, c, e

For optimal airway examination in obese patients, the following should be noted: neck circumference, MP score, thyromental distance, assessment of mouth opening and jaw protrusion, range of neck movement and general assessment of craniofacial architecture. The presence of a cervical fat pad or ‘hump’ should also be noted as this can lead to difficulty in positioning the patient optimally for intubation.

5.Answers b, c, e

Some authors and many centres still advocate rapid sequence induction (RSI) with cricoid pressure in all morbidly obese patients, although this practice is now controversial. Patients who have previously undergone bariatric surgery, have anatomical and physiological changes in the stomach which appear to increase the risk of aspiration when compared with non-bariatric patients. Obesity is associated with a reduction in the time to desaturation after apnoea. Pre-oxygenation in the head-up or sitting, rather than the supine position increases functional residual capacity (FRC) allowing a higher oxygen tension to develop resulting in a clinically significant increase in the desaturation safety period and allows greater time for airway control and intubation.

6.Answers a, e

It is associated with oestrogen dependent cancers breast uterus and prostate.

7.Answers b, d

Reduced appetite. The main weight gain is fluid retention.

8.Answers a, d, e

Type 2 diabetes hyperlipidaemia, hypercoagulability.

9.Answers a, b, e

Problems include mal-absorption (protein calorie malnutrition (7%)), and diarrhoea. Long term nutritional implications with risk of anaemia and bone demineralisation. Reserved for patients with super morbid obesity (BMI

kg/m2) as highly effective. Other complications include reports of stomal ulceration (12.5%) and dumping syndrome now reduced if the pylorus is intact.

10.Answers c e

The laparoscopic Roux-en-Y gastric bypass (LRYGB) is considered a combination of both restriction and mild mal-absorption.

11.Answers a, e

12.Answers. a, c e

Ghrelin is primarily secreted by neuroendocrine cells of the gastric fundus. Suppressed by LRYGB. Changes in vagal control as a result of the gastric bypass, may result in lowering of ghrelin levels and hence weight loss.

13.Answers a b c d e

Overeating is the most common cause by far. Insulinoma, a rare insulin producing islet cell tumour, is associated with symptomatic hypoglycaemia. Significant weight gain as sufferers learn to eat regular snacks to avoid symptoms. Craniopharyngioma, langerhans histiocytosis and sarcoidosis can present with weight gain due to disruption of hypothalamic neuro-circuits involved in regulation of energy balance. Monogenic obesity – onset of obesity in the pre-school years, hyperphagia. Leptin deficiency can be treated with subcutaneous leptin and reverses both the obesity syndrome and associated endocrine effects, but so far only a handful of families with this condition have been identified worldwide

14.Answers a. e

Orlistat has beneficial effects on LDL-cholesterol, reduces blood pressure, HbA1c in diabetes, serum triglycerides and waist circumference. 37% reduction in the risk of developing diabetes in those treated with Orlistat over the 4 year trial period. Satiety can be induced by inhibiting reuptake of serotonin. Orlistat and Sibutramine have been reported to assist in a greater than 10% weight loss in 12–18% of the treated groups in clinical trials lasting over one year.

15.Answers c. d e

Weight gain may be an adverse effect with oral sulphonylureas (eg glibenclamide, gliclazide) and glitazones (rosiglitazone, pioglitazone) but also with subcutaneous insulin with either a basal or multiple injection regimen. Glucagon-like peptide-1 (GLP-1) agonist, exenatide (BYETTA trade name), is the first available incretin mimetic. oral dipeptidyl peptidase-4 (DPP-4) inhibitors such as sitagliptin or vildagliptin, also act on the incretin system, prolonging the half-life of endogenous GLP-1 by inhibiting breakdown by the enzyme DPP-4. GLP-1 is also a powerful incretin, promoting glucose-dependent insulin secretion in response to a meal and reducing glucagon secretion from pancreatic alpha cells.

16.Answers b, c, d, e.

Both beta-blockers and thiazide diuretics may worsen glucose tolerance and dyslipidaemia.

17.Answers b, c

Often but not necessarily associated with a drop in oxygen saturation. Obesity is an important risk factor. There is a particular association between OSAHS and a visceral pattern of obesity, classically seen in men who are prone to deposition of fat within the abdominal wall and viscera (“apples”). By contrast, the classically female subcutaneous deposition of fat, often localised around the hips (“pears”) confers less tendency to sleep disordered breathing.

18.Answers a. e

Symptoms of the condition do not correspond closely to the severity of the disease. Chronic pulmonary hypertension leads to the development of right heart failure. Obstructive episodes occur during the periods of profound loss of muscle tone that accompany Rapid Eye Movement (REM) sleep but in more severe cases will occur throughout other sleep patterns as well. Effects on the brainstem reflexes cause bradycardias, arrhythmias and hypertensive surges.

19.Answers d

Palatal surgery is often touted as a cure for OSA, despite absence of demonstrable benefit in numerous meta-analyses. Tonsillar hypertrophy is an indication for surgery in children, in whom normal sleep pattern is restored in 87%

20.Answers a c e

Less splenic injury but more post-operative small bowel obstruction with laparoscopy. Podnos YD, Arch Surg 2003;138(9);957–61.

SAQ answers

1.Describe the pathophysiology of Obese hypoventilation.

Answer: Obesity has a wide range of effects throughout the cardiorespiratory system.

The physical space in the oro-pharynx is reduced by excessive tissue volumes, such as large tonsils, large tongue. The proportion of fat in the tongue correlates with adiposity, being up to 30% in the obese.

Increased chest wall thickness reduces chest wall compliance as well as increasing the work of moving the chest wall. This will tend to reduce resting lung volume, and hence increase airway resistance. Obese hypo ventilators also have higher upper airway resistance Lung function may show a moderate restrictive defect caused by loss of expiratory reserve volume.

There is a blunted central responsiveness to hypercapnia and hypoxia. This is associated with leptin resistance. Leptin is a satiety protein that increases ventilation.

Obstructive sleep apnoea, is common with prolonged periods of hypoventilation, typically of 20

minutes duration or more. There may be profound oxygen desaturation during such episodes especially during REM sleep. Note that the diaphragm is unaided by the intercostals and accessory musculature, which are atonic in the REM state. The apnoea or hypopnoea leads to a fall in arterial oxygen and a rise in arterial carbon dioxide. This has subsequent effects upon brainstem reflexes causing bradycardias, arrhythmias and hypertensive surges, both systemic and pulmonary.

The obese hypoventilation state tends to accumulate CO2 steadily throughout the night. There are associated cardiovascular changes with a tendency to pulmonary hypertension and right ventricular failure. Cor pulmonale as seen by peripheral oedema is also seen with CO2 retention.

Morning headache is a symptom strongly associated with nocturnal CO2 retention. Somnolence tends to be a problem.

Tsuiki S, Isono S, Ishikawa T, Yamashiro Y, Tatsumi K, Nishino T. Anatomical balance of the upper airway and obstructive sleep apnea. Anesthesiology 2008;108(6):1009–15.

Lin CC, Wu KM, Chou CS, Liaw SF. Oral airway resistance during wakefulness in eucapnic and hypercapnic sleep apnea syndrome. Respir Physiol Neurobiol 2004;139(2):215–24.

Becker HF, Piper AJ, Flynn WE, McNamara SG, Grunstein RR, Peter JH, et al. Breathing during sleep in patients with nocturnal desaturation. Am J Respir Crit Care Med 1999;159(1):112–8.

Ragette R, Mellies U, Schwake C, Voit T, Teschler H. Patterns and predictors of sleep disordered breathing in primary myopathies. Thorax 2002;57(8):724–8.

2.What are the useful things to look for that might predict a difficult intubation in the obese?

Answer: In addition to a general medical history, factors that are suggestive of difficulty with intubation include suspected or diagnosed obstructive sleep apnoea (OSA), problems with previous anaesthetics and airway management, and a history of craniofacial, dental or neck problems. The presence of treated or untreated gastro-oesophageal reflux disease (GORD) or previous bariatric surgery should be noted as this may also influence the airway management strategy.

The review of previous anaesthetic records should look for any reports of difficult facemask ventilation, repeated attempts at intubation, prolonged intubation time, Cormack & Lehane grade 3 or 4, advanced airway techniques and devices used, problems encountered despite management by experienced anaesthetist and an intubation difficulty scale (IDS) score >5.

Features in the examination to look for include a reduced thyromental distance (<6

cm), a Mallampati score or 3 or 4 and increased neck circumference. There should also be an assessment of mouth opening, jaw protrusion, range of neck movement and general assessment of craniofacial architecture looking for flattened, compressed anterior–posterior dimensions, retrognathism, relative macroglossia, and a narrow or bulky oro-pharynx. The presence of a cervical fat pad or ‘hump’ should also be noted as this can lead to difficulty in positioning the patient for intubation.

Clinical scenario answers

1.What would constitute appropriate pre-operative investigations in this patient?

Blood tests: Thyroid function tests and HbA1C.

Sleep study: To ensure OSA is well controlled on current/appropriate CPAP settings and/or to assess patient compliance.

Cardiorespiratory Investigation: ECG as high risk of ischaemic heart disease, echocardiogram to assess for signs of pulmonary hypertension and right heart failure (secondary to OSA) if clinically indicated from patient examination. Consider CPEX testing as patient falls into very high risk group (male, >45 years, BMI >50 and hypertension) for morbidity and mortality following gastric bypass surgery. If unable to exercise consider pharmacological stress testing instead.

2.Is intubation likely to be difficult in this patient?

Yes. Male patients with large neck circumference and a history of OSA are generally more difficult to intubate. Consideration should be given to awake fibre-optic intubation. If proceeding with intravenous induction of general anaesthesia, ensure readily available senior help and difficult airway equipment/algorithim.

3.What are the main considerations for intravenous induction and removal of gastric balloon?

Consideration should be given to pre-medication with an H2 receptor antagonist or proton pump inhibitor. The patient should be placed in the sitting or ramped position and should be pre-oxygenated with application of CPAP/PEEP, to increase time to desaturation following induction. Rapid sequence induction should be performed with cricoid pressure as the 500

ml intra-gastric balloon increases risk of regurgitation and aspiration. Once tracheal intubation is successful, the endoscopic approach for balloon removal risks tube displacement so ensure this is secured appropriately throughout.

4.What are the possible intra-operative surgical problems?

The typical male or android distribution of fat often results in difficult surgical access. Also, there may be extensive adhesions from previous open cholecystectomy. Duration of surgery may thus be significantly prolonged and conversion to open technique may be necessary.

5.What are the possible intra-operative anaesthetic problems?

Due to high BMI, truncal fat distribution and pneumoperitoneum, effective ventilation may be difficult with high airway pressures, small tidal volumes and rising arterial pCO2. Use protective ventilation strategies along with PEEP to improve oxygenation.

6.What are the most likely post-operative complications in this case?

Airway obstruction and acute respiratory failure are more likely because of diagnosis of OSA and probable sensitivity to opioid central depressant effects. Particularly hazardous is the use of intravenous opioids/PCA for post-operative pain control. Thus, continuous ECG and pulse oximetry are mandatory on the first post-operative night to monitor any desaturation and associated dysrhythmias. Such patients should therefore be managed post-operatively in a bariatric care setting or high dependency unit, with skilled and experienced staff in attendance.

This patient is also at high risk of venous thrombo-embolism and good, multimodal prophylaxis is required.

PII: S0953-7112(09)00124-0

doi:10.1016/j.cacc.2009.10.007

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